U.S. patent application number 13/321884 was filed with the patent office on 2012-03-22 for glazing with very little double imaging.
This patent application is currently assigned to SAINT-GOBAIN GLASS FRANCE. Invention is credited to Jean-Luc Lesage, Corinne Payen, Herve Thellier.
Application Number | 20120070624 13/321884 |
Document ID | / |
Family ID | 41467297 |
Filed Date | 2012-03-22 |
United States Patent
Application |
20120070624 |
Kind Code |
A1 |
Payen; Corinne ; et
al. |
March 22, 2012 |
GLAZING WITH VERY LITTLE DOUBLE IMAGING
Abstract
The invention relates to a curved glass pane, made of float
glass, the area of a main face of which is greater than 1.5 m.sup.2
and the product of its two depths of bending is greater than 3000
mm.sup.2, and such that its point located on the normal to its
surface passing through its center of gravity has a radius of
curvature of less than 3 m in any direction, the variation in its
thickness in the longitudinal float direction being less than 10
.mu.m over 500 mm. This pane may be assembled into laminated
glazing of the automobile windshield type. Such a windshield has a
very small amount of double imaging even when it is fitted into the
vehicle so as to be close to the horizontal.
Inventors: |
Payen; Corinne; (Montmacq,
FR) ; Thellier; Herve; (Pimprez, FR) ; Lesage;
Jean-Luc; (Compiegne, FR) |
Assignee: |
SAINT-GOBAIN GLASS FRANCE
Courbevoie
FR
|
Family ID: |
41467297 |
Appl. No.: |
13/321884 |
Filed: |
May 19, 2010 |
PCT Filed: |
May 19, 2010 |
PCT NO: |
PCT/FR2010/050975 |
371 Date: |
November 22, 2011 |
Current U.S.
Class: |
428/172 ;
428/156; 65/106 |
Current CPC
Class: |
Y10T 428/24628 20150115;
C03B 23/023 20130101; Y10T 428/24479 20150115; B32B 17/10036
20130101; Y10T 428/24612 20150115; B32B 17/10761 20130101; C03B
23/0252 20130101; B60J 1/008 20130101 |
Class at
Publication: |
428/172 ;
428/156; 65/106 |
International
Class: |
B32B 17/00 20060101
B32B017/00; C03B 23/025 20060101 C03B023/025; C03B 23/023 20060101
C03B023/023 |
Foreign Application Data
Date |
Code |
Application Number |
May 27, 2009 |
FR |
0953505 |
Claims
1. A curved glass pane, comprising float glass, wherein an area of
a main face is greater than 1.5 m.sup.2, a product of two depths of
bending of the glass pane is greater than 3000 mm.sup.2, a point
located on the normal to a surface passing through the center of
gravity of the glass pane has a radius of curvature of less than 3
m in any direction, and a variation in the thickness of the glass
pane in the longitudinal float direction is less than 10 .mu.m over
500 mm.
2. The pane of claim 1, wherein the variation in the thickness is
less than 7 .mu.m over 500 mm in the longitudinal float
direction.
3. The pane of claim 1, wherein the area of a main face is greater
than 1.8 m.sup.2.
4. The pane of claim 1, wherein the product of two depths of
bending is greater than 6000 mm.sup.2, and the point located on the
normal to a surface passing through the center of gravity has a
radius of curvature of less than 2 m in any direction.
5. The pane of claim 1, wherein a thickness of the glass pane
ranges from 1.1 to 2.8 mm.
6. A laminated glazing assembly, comprising at least two glass
panes of claim 1, wherein float directions of the at least two
glass panes are mutually concordant.
7. The glazing assembly of claim 6, wherein a measured level of
double imaging: through the point on the normal to a surface
passing through the center of gravity; and at a viewing angle of
20.degree., is at most 7 minutes.
8. A windshield, comprising the glazing of claim 7.
9. A motor vehicle, comprising the windshield of claim 8, wherein a
transverse float direction is horizontal.
10. A process for manufacturing the curved glass pane of claim 1,
the process comprising bending a pane against a solid mold to give
the pane at least 50% of each of the two depths of bending.
11. The process of claim 10, wherein a temperature of the pane at
the point located on the normal to a surface passing through the
center of gravity is between 590 and 615.degree. C. during the
bending.
12. The process of claim 11, further comprising cooling directly
after the bending.
13. The process of claim 10, further comprising a gravity bending
before the bending of the pane against the solid mold.
14. The process of claim 13, wherein, during the gravity bending, a
temperature of the pane at the point located on the normal to a
surface passing through the center of gravity is between 610 and
640.degree. C.
15. The process of claim 10, wherein at least two superposed glass
panes are bent simultaneously.
Description
[0001] The invention relates to the field of glazing, especially
automotive glazing, with very little double imaging.
[0002] Automotive glazing, especially of the windshield or rear
window type, must have the smallest number of optical defects for
both safety reasons and esthetic reasons. The vision of a driver
must be as clear as possible and it is in particular unacceptable
for the image that he perceives of the environment of the
automobile to be a double image. Multiple imaging as perceived by
the driver through the windshield is a known phenomenon stemming
from multiple reflections at the air/glass interfaces. It is
generally referred to as double imaging even though in theory other
additional images exist, since these additional images are of very
low intensity. An additional reflection is accompanied in fact by a
substantial loss of intensity of the parasitic image, by a factor
of the order of 100 relative to the intensity of the main image.
The magnitude of the phenomenon increases with the angle of
inclination of the glazing.
[0003] The theoretical amount of double imaging, which is expressed
as a number in minutes by those skilled in the art, can be
calculated by computer. This amount depends on many factors, such
as the thickness of the panes constituting the windshield and on
the local curvature, but also on the angle of viewing through the
glazing. A distinction is made between the amount of vertical
double imaging (the images appearing one above the other when a
person is sitting in the vehicle) and the amount of horizontal
double imaging (the images appear one beside the other when a
person is sitting in the vehicle). The usual inclination of the
windshield generates vertical double imaging, whereas in general
there is no horizontal double imaging problem. The closer the
glazing is to the horizontal on the motor vehicle (as for example
in FIG. 3), the greater the amount of vertical double imaging. At
the present time, the maximum acceptable amount of double imaging
(in all directions) is considered to be 7 minutes, as this is
deemed to be imperceptible by the human eye. It is the amount of
vertical double imaging that is difficult to contain to within at
most 7 minutes in the case of glazing which is highly inclined in
the use position. The amount of double imaging may be measured
using the target test technique or the collimation telescope test
technique as described in Rule 43, Addition 42 of the E/ECE/324 or
E/ECE/TRANS/505 agreement, relating to the adoption of uniform
technical requirements applicable to wheeled vehicles, to equipment
and to components that can be mounted or used on a wheeled vehicle,
and the conditions for reciprocal recognition of homologations
granted in accordance with these provisions.
[0004] Automobile manufacturers, especially French ones, seek to
design ever more innovative models. In particular, the windshields
designed may be very large, since sometimes they may even form part
of the roof by going over the top of front passengers. These
windshields are also increasingly inclined to the horizontal.
Moreover, their curvatures must be very regular so as to merge into
the general shape of the automobile.
[0005] In the context of developing such windshields, it has been
discovered that the amount of vertical double imaging is greater
than the theoretical amount of double imaging without knowing the
reason why. The windshields in question have been produced by a
gravity bending process, which theoretically should be very
suitable for forming them. The amount of vertical double imaging
was more than 50% greater than the theoretical amount of double
imaging.
[0006] Many bending processes have already been described, such as
gravity bending as in EP 0 448 447, EP 0 705 798 and WO
2004/103922, bending by running glass between conveying rollers as
in WO 2004/033381 or WO 2005/047198, and bending by pressing glass
against a solid mold, said pressing being carried out either using
a frame, as in U.S. Pat. No. 5,974,836, WO 95/01938, WO 02/06170 or
WO 2004/087590, or by suction as in WO 02/064519 or WO
2006/072721.
[0007] The present invention is based on the discovery that such
large glazing highly curved in all directions in the central zone
exhibits a large amount of double imaging when it is produced by
gravity bending, whereas it exhibits double imaging much closer to
the theoretical amount when it is produced by pressing against a
solid mold. Without these explanations limiting the scope of the
invention, it seems that the gravity process produces a slight
thinning of the glass pane in the central zone so that the two
faces of the pane are not in fact strictly parallel but form a very
slight prism. The variations in question are very small, around 40
to 50 .mu.m, but this is sufficient for the double imaging to be
magnified very perceptibly for the human eye, especially when the
windshield is highly inclined. This drawback stems from the
combination of the following factors: high curvatures in all
directions; large size; use of a gravity process that in particular
entails higher bending temperatures. The high angle of inclination
of the glazing on the motor vehicle further accentuates the
phenomenon.
[0008] It is also necessary to take into consideration the fact
that the variation in thickness of the initial flat glass (float
glass, manufactured by floating the glass on molten metal) has an
influence on the thickness variation of the bent glass. Float glass
generally has a larger thickness variation in the transverse
direction than in the longitudinal direction. The longitudinal
direction of float glass corresponds to the direction in which the
glass runs through the float glass plant. The transverse and
longitudinal directions of a float glass are very easily identified
using a shadowgraph technique by virtue of lines corresponding to
the longitudinal direction. Thus, a float glass is perfectly
identifiable by these lines and by the fact that one of its faces
is enriched with tin. In the context of the present invention, a
float glass having a thickness variation of less than 50 .mu.m for
500 mm in the transverse direction and less than 2 .mu.m for 500 mm
in the longitudinal direction is used before bending. For optical
transmission quality reasons, the glazing is generally placed on
the motor vehicle so that the transverse direction of the glass
corresponds to the horizontal.
[0009] By virtue of the invention, the thickness variation of a
pane of float glass bent in the longitudinal direction can be
reduced to less than 10 .mu.m over 500 mm and even less than 7
.mu.m over 500 mm, thereby reducing the amount of double imaging in
the vertical direction (or longitudinal direction relative to the
float direction) to at most 7 minutes with a 20.degree. viewing
angle (i.e. the angle between the horizontal and a longitudinal
chord passing through the middle of two transverse bands).
[0010] The thicknesses (and therefore the thickness variations) may
be measured using a micrometer or a contactless sensor, especially
a confocal optical sensor. This applies both for individual glass
panes and for the assembled glazing.
[0011] The glazing according to the invention is curved along two
mutually orthogonal directions and therefore has two depths of
bending. A person skilled in the art of automotive glazing terms
the largest depth of transverse bending (relative to the motor
vehicle) the "sag" and terms the largest depth of longitudinal
bending (relative to the motor vehicle) the "second depth of
bending".
[0012] The glazing, especially of the automobile windshield type,
generally comprises overall four sides or "bands".
[0013] The glazing to which the present invention relates is large,
its width generally being greater than 1.10 m and its length
generally being greater than 1.10 m or even greater than 1.3 m. In
addition, it has the following characteristics (as does each glass
pane from which it is made): [0014] a) its area (of one of its main
faces) is greater than 1.5 m.sup.2 and may even be greater than 1.6
m.sup.2 or even greater than 1.8 m.sup.2; [0015] b) the product of
its two depths of bending is greater than 3000 mm.sup.2 and may
even exceed 5000 mm.sup.2 or even 8000 mm.sup.2; and [0016] c) the
point on the glazing located on the normal to its surface and
passing through its center of gravity has a radius of curvature of
less than 3 m and even less than 2.5 m in any direction.
[0017] Condition a) above means that the glazing is large both in
width and in length. Condition b) means that the glazing is highly
curved in all directions. Condition c) means that the glazing is
highly and uniformly curved in all directions in a central region
essential for vision. This is because a glazing assembly may have a
high sag and high counter-bending without its curvature being too
pronounced in the central region, as shown in FIG. 2a). This type
of shape is quite common and easy to obtain by gravity forming. The
sagging of the region close to the edges is called the "bath
effect" by those skilled in the art. The central region is only
slightly curved. This type of shape is considered today to be
somewhat unattractive. It is known to avoid this bath effect in a
gravity process by providing an internal zone support as taught in
WO 2004/103922.
[0018] Thus, the invention firstly relates to a curved glass pane,
made of float glass, the area of a main face of which is greater
than 1.5 m.sup.2 and the product of its two depths of bending is
greater than 3000 mm.sup.2, and such that its point located on the
normal to its surface, said normal passing through its center of
gravity, has a radius of curvature of less than 3 m in any
direction, the variation in its thickness in the longitudinal float
direction being less than 10 .mu.m over 500 mm and preferably less
than 7 .mu.m over 500 mm.
[0019] In general, the area of a main face of the glass pane is
less than 3 m.sup.2.
[0020] The product of its two depths of bending may be greater than
6000 mm.sup.2 but is generally less than 150 000 mm.sup.2.
[0021] The point on the glazing located on the normal to its
surface, said normal passing through its center of gravity, may
have a radius of curvature of less than 2 m in any direction and is
generally greater than 1 m.
[0022] According to the invention, the large glazing pane according
to the invention is bent by forming it on a solid bending mold, it
being possible for the force with which the glass is pressed
against said mold to be of mechanical or pneumatic nature. If the
force is of mechanical nature, it may be applied by a solid or
frame-shaped counter-mold. In particular, it may be a frame as
shown by reference (4) in FIG. 1 of WO 95/01938 or the segmented
frame referenced (9, 10, 11, 12) in FIGS. 1 and 2 of U.S. Pat. No.
5,974,836. If the force is of pneumatic nature, it may be applied
by suction through the solid mold by virtue of holes in the surface
with which the glass is in contact with said solid mold, as shown
in FIG. 2 of WO 2006/072721. A pneumatic force may also be applied
by means of a skirt surrounding the solid mold as in the model of
the skirt referenced 16 in FIG. 2 of WO 04/087590. The skirt
provides a suction force that generates a flow of air surrounding
the pane, passing over its edge. However, the pneumatic force
exerted by a skirt is generally insufficient and is preferably
supplemented with a mechanical or pneumatic force through the solid
mold.
[0023] The bending against a solid mold takes place at least at the
end of bending, that is to say just before cooling. This bending
against a solid mold is therefore followed directly (that is to say
without a particular additional bending step) by a cooling step,
generally natural cooling, generally placed on a frame.
[0024] This bending against the solid mold gives the glazing at
least 50% of each of the two final depths of bending, or even at
least 60% of each of the two final depths of bending. These two
depths of bending correspond to the sag and to the second depth of
bending as already explained. In general, these two depths of
bending correspond to mutually orthogonal bending directions and
one of these two depths is the largest depth of bending of the
pane.
[0025] The forming against a solid mold may be preceded by bending
using another process, especially and preferably by gravity
bending. The existence of gravity prebending is even preferred as
it makes it possible in the end to increase the complexity of the
glazing (larger depths of bending in all directions), without
degrading the optical quality. This gravity bending is carried out
on a support of the frame or skeleton type, especially of the
double skeleton type (see EP 0 448 447, EP 0 705 798 and WO
2004/103922). This preliminary bending (or prebending) gives the
glazing less than 50% of each of the two final depths of bending or
even less than 40% of each of the two final depths of bending.
[0026] The bending against a solid mold is preferably carried out
in such a way that the glass, at the point located on the normal to
its surface passing through its center of gravity, is at a
temperature between 590 and 615.degree. C.
[0027] The optional preliminary gravity bending is preferably
carried out in such a way that the glass, at the point located on
the normal to its surface passing through its center of gravity, is
at a temperature between 610 and 640.degree. C.
[0028] For all the bending steps, the various glass panes intended
to be assembled into the same final laminated glazing (generally
there are two panes) are generally superposed and bent together
simultaneously. An interlayer powder is placed between the various
panes, as is known to those skilled in the art, in order to
minimize their tendency to stick together.
[0029] It is considered that the point on the laminated glazing
located on the normal to its surface, said normal passing through
the center of gravity of said glazing, is substantially at the same
place as the point on each of the panes of the glazing located on
the normal to the surface of each pane and passing through the
center of gravity of said pane.
[0030] The thickness variation of each curved glass pane according
to the invention is less than 10 .mu.m, preferably less than 7
.mu.m and even less than 3 .mu.m over 500 mm in the longitudinal
float direction. This thickness variation is the difference between
the largest thickness and the smallest thickness of the pane over a
distance of 500 mm on the surface in the longitudinal direction.
Before bending, the glass pane is flat and has a thickness
variation of less than 2 .mu.m over 500 mm in the longitudinal
float direction.
[0031] The glass pane generally has a thickness ranging from 1 to 4
mm and more generally from 1.1 to 2.8 mm.
[0032] The sheet of polymer (generally polyvinyl butyral or PVB)
inserted between two glass panes within the laminated glazing
generally has a thickness ranging from 0.3 to 1.6 mm.
[0033] The glass panes are assembled into laminated glazing in such
a way that the float directions (or orientations) of the panes are
mutually concordant. Thus, the invention also relates to laminated
glazing comprising several curved panes according to the invention
(generally two panes), said glazing having a measured level of
double imaging: [0034] through the point on its surface located on
the normal to its surface passing through its center of gravity and
[0035] at a viewing angle of 20.degree., of at most 7 minutes. This
glazing is intended for fitting into all kinds of vehicle and
especially motor vehicles. The transverse float direction of the
glass panes assembled in the glazing corresponds to the horizontal
in the case of the vehicle.
[0036] FIG. 1a) illustrates what is meant by the sag F and the
width l of glazing 1 in the position in which it is fitted into a
motor vehicle. The sag F, i.e. the largest depth of transverse
bending, is the length of the largest segment having as ends the
middle of a transverse arc 4 and the middle of the chord 5
corresponding thereto, said chord here being the width l of the
glazing. This glazing has overall four bands (or sides), two
transverse bands 21 and 22 and two longitudinal bands 23 and
24.
[0037] FIG. 1b) illustrates what is meant by the second depth of
bending DB and the length L of a glazing 1. The second depth of
bending DB, i.e. the largest depth of longitudinal bending, is the
length of the largest distance between a point on a longitudinal
arc 2 (passing through the middles of the two transverse bands 21
and 22) and the chord 3 corresponding thereto (this chord is also
here the length L of the glazing). The transverse bands 21 and 22
have middles 25 and 26 respectively.
[0038] FIG. 2 compares two glazing assemblies having the same depth
of bending 7 while being very different in terms of curvature in
the central region 8 and 9 respectively. The glazing assembly 10 of
FIG. 2a) is quite flat in the central region 8, whereas the glazing
assembly 11 of FIG. 2b) is more curved in the central region 9,
this going hand in hand with a more harmonious shape, better wiping
quality and being better suited to the general shape of current
automobiles.
[0039] FIG. 3 shows a glazing assembly 12 as fitted into a motor
vehicle in cross section through its longitudinal arc passing in
its vertical plane of symmetry (this is the arc 2 of FIG. 1b)
passing through the middles 25 and 26 of the two transverse bands
21 and 22), and the angle .alpha. of 20.degree. (viewing angle)
below which the amount of vertical double imaging is measured. The
amount of vertical double imaging is measured at an angle .alpha.
of 20.degree. between the horizontal line 13 and the chord 14 of
the longitudinal arc passing through the middle of the transverse
bands (this is the chord 3 in FIG. 1b), which passes through the
middles 25 and 26 of the transverse bands 21 and 22). The
horizontal line 13 corresponds substantially to the viewing
direction of passengers in the motor vehicle.
EXAMPLES
[0040] Identical windshields were manufactured from batches of
identical float glass panes but by using two different bending
processes. Two versions were manufactured: one was very large
(called "TG") and the other was of more normal size (called "N").
The dimensions of these windshields were the following: [0041] very
large windshield (TG): [0042] length L: 1.48 m; [0043] width l: 1.4
m (horizontal when the windshield is fitted into the automobile);
[0044] L.times.l: 2.072 m.sup.2; [0045] sag F: 103 mm; [0046]
second depth of bending DB: 105 mm; [0047] F.times.DB: 10815
mm.sup.2; [0048] largest radius of curvature at the point P located
on the normal to the surface passing through the center of gravity:
1500 mm. [0049] Normal windshield (N): [0050] length L: 1.1 m;
[0051] width l: 1.2 m (horizontal when the windshield is fitted
into the automobile); [0052] L.times.l: 1.32 m.sup.2; [0053] sag F:
80 mm; [0054] second depth of bending DB: 25 mm; [0055] F.times.DB:
2000 mm.sup.2; [0056] largest radius of curvature at the point P
located on the normal to the surface passing through the center of
gravity: 3500 mm.
[0057] The windshields were laminated and comprised two glass panes
each 2.1 mm in thickness separated by a sheet of PVB 0.76 mm in
thickness. In both cases, the two glass panes were bent together,
by being superposed.
[0058] The glazing N was formed by conventional gravity bending
using a double-skeleton of the type described in FIG. 3 of WO
04/103922. For Comparative Example 2, the windshield G was formed
by gravity bending using a multi-support skeleton, including an
internal zone support so as to avoid any bath effect, on the
principle shown in FIG. 9 of WO 04/103922. For Comparative Example
3, the windshield TG was firstly formed by gravity bending using a
single skeleton at a temperature of 620.degree. C. until a sag
representing 30% of the final sag was obtained and until a second
depth of bending representing 50% of the final second depth of
bending was obtained. The glazing thus prebent was then subjected
to a forming operation by pressing it against a solid mold on the
principle of the process shown in FIG. 2 of WO 04/087590 at
600.degree. C.
[0059] The thickness variation of each glass pane was measured
before assembly using a confocal optical sensor.
[0060] Two glass panes were then joined together as laminated
glazing with an intermediate PVB sheet in a manner known to those
skilled in the art.
[0061] The amount of double imaging was measured on the laminated
glazing at point P located on the normal to the surface passing
through the center of gravity of the glazing, with a viewing angle
.alpha. of 20.degree. between the horizontal and the longitudinal
chord joining the two points of the glazing at mid-distance of the
two transverse bands. The amount of double imaging was measured
using the target test technique or the collimation telescope test
technique as described in the ECE R43 regulation.
[0062] Table 1 gives the results. The temperatures indicated in
this table are those of each glass pane at the point P located on
the normal to the surface passing through the center of
gravity.
TABLE-US-00001 TABLE 1 1 2 (comparative (comparative Example
example) example) 3 Windshield size N TG TG Bending type Gravity
Gravity Gravity then pressing Glass temperature 632.degree. C.
632.degree. C. 590.degree. C. at the end of bending Thickness 6
.mu.m 15 .mu.m 5.6 .mu.m variation of each glass pane in the
longitudinal direction over 500 mm Amount of 7 min 10 min 6 min
vertical double imaging of the laminated glazing at an angle of
20.degree.
* * * * *